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        <div id="links">
          <a href="Carp.html">Carp</a>
          <div id="more">
            (<a href="Carp.txt">source</a>,
            <a href="https://metacpan.org/pod/Carp">CPAN</a>)
          </div>
            <div id="moduleversion">version 1.52</div>
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          You are viewing the version of this documentation from Perl 5.35.0.
            This is a development version of Perl.
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        <h1><a id="toc">CONTENTS</a></h1>
                  <ul>
              <li>
                <a class="text-decoration-none" href="Carp.html#NAME">NAME</a>
              </li>
              <li>
                <a class="text-decoration-none" href="Carp.html#SYNOPSIS">SYNOPSIS</a>
              </li>
              <li>
                <a class="text-decoration-none" href="Carp.html#DESCRIPTION">DESCRIPTION</a>
                            <ul>
              <li>
                <a class="text-decoration-none" href="Carp.html#Forcing-a-Stack-Trace">Forcing a Stack Trace</a>
              </li>
              <li>
                <a class="text-decoration-none" href="Carp.html#Stack-Trace-formatting">Stack Trace formatting</a>
              </li>
          </ul>

              </li>
              <li>
                <a class="text-decoration-none" href="Carp.html#GLOBAL-VARIABLES">GLOBAL VARIABLES</a>
                            <ul>
              <li>
                <a class="text-decoration-none" href="Carp.html#$Carp::MaxEvalLen">$Carp::MaxEvalLen</a>
              </li>
              <li>
                <a class="text-decoration-none" href="Carp.html#$Carp::MaxArgLen">$Carp::MaxArgLen</a>
              </li>
              <li>
                <a class="text-decoration-none" href="Carp.html#$Carp::MaxArgNums">$Carp::MaxArgNums</a>
              </li>
              <li>
                <a class="text-decoration-none" href="Carp.html#$Carp::Verbose">$Carp::Verbose</a>
              </li>
              <li>
                <a class="text-decoration-none" href="Carp.html#$Carp::RefArgFormatter">$Carp::RefArgFormatter</a>
              </li>
              <li>
                <a class="text-decoration-none" href="Carp.html#@CARP_NOT">@CARP_NOT</a>
              </li>
              <li>
                <a class="text-decoration-none" href="Carp.html#%25Carp::Internal">%Carp::Internal</a>
              </li>
              <li>
                <a class="text-decoration-none" href="Carp.html#%25Carp::CarpInternal">%Carp::CarpInternal</a>
              </li>
              <li>
                <a class="text-decoration-none" href="Carp.html#$Carp::CarpLevel">$Carp::CarpLevel</a>
              </li>
          </ul>

              </li>
              <li>
                <a class="text-decoration-none" href="Carp.html#BUGS">BUGS</a>
              </li>
              <li>
                <a class="text-decoration-none" href="Carp.html#SEE-ALSO">SEE ALSO</a>
              </li>
              <li>
                <a class="text-decoration-none" href="Carp.html#CONTRIBUTING">CONTRIBUTING</a>
              </li>
              <li>
                <a class="text-decoration-none" href="Carp.html#AUTHOR">AUTHOR</a>
              </li>
              <li>
                <a class="text-decoration-none" href="Carp.html#COPYRIGHT">COPYRIGHT</a>
              </li>
              <li>
                <a class="text-decoration-none" href="Carp.html#LICENSE">LICENSE</a>
              </li>
          </ul>

      <h1 id="NAME"><a class="permalink" href="Carp.html#NAME">#</a>NAME</h1>

<p>Carp - alternative warn and die for modules</p>

<h1 id="SYNOPSIS"><a class="permalink" href="Carp.html#SYNOPSIS">#</a>SYNOPSIS</h1>

<pre><code>use Carp;

# warn user (from perspective of caller)
carp &quot;string trimmed to 80 chars&quot;;

# die of errors (from perspective of caller)
croak &quot;We&#39;re outta here!&quot;;

# die of errors with stack backtrace
confess &quot;not implemented&quot;;

# cluck, longmess and shortmess not exported by default
use Carp qw(cluck longmess shortmess);
cluck &quot;This is how we got here!&quot;; # warn with stack backtrace
$long_message   = longmess( &quot;message from cluck() or confess()&quot; );
$short_message  = shortmess( &quot;message from carp() or croak()&quot; );</code></pre>

<h1 id="DESCRIPTION"><a class="permalink" href="Carp.html#DESCRIPTION">#</a>DESCRIPTION</h1>

<p>The Carp routines are useful in your own modules because they act like <code>die()</code> or <code>warn()</code>, but with a message which is more likely to be useful to a user of your module. In the case of <code>cluck()</code> and <code>confess()</code>, that context is a summary of every call in the call-stack; <code>longmess()</code> returns the contents of the error message.</p>

<p>For a shorter message you can use <code>carp()</code> or <code>croak()</code> which report the error as being from where your module was called. <code>shortmess()</code> returns the contents of this error message. There is no guarantee that that is where the error was, but it is a good educated guess.</p>

<p><code>Carp</code> takes care not to clobber the status variables <code>$!</code> and <code>$^E</code> in the course of assembling its error messages. This means that a <code>$SIG{__DIE__}</code> or <code>$SIG{__WARN__}</code> handler can capture the error information held in those variables, if it is required to augment the error message, and if the code calling <code>Carp</code> left useful values there. Of course, <code>Carp</code> can&#39;t guarantee the latter.</p>

<p>You can also alter the way the output and logic of <code>Carp</code> works, by changing some global variables in the <code>Carp</code> namespace. See the section on <code>GLOBAL VARIABLES</code> below.</p>

<p>Here is a more complete description of how <code>carp</code> and <code>croak</code> work. What they do is search the call-stack for a function call stack where they have not been told that there shouldn&#39;t be an error. If every call is marked safe, they give up and give a full stack backtrace instead. In other words they presume that the first likely looking potential suspect is guilty. Their rules for telling whether a call shouldn&#39;t generate errors work as follows:</p>

<ol>

<li><p>Any call from a package to itself is safe.</p>

</li>
<li><p>Packages claim that there won&#39;t be errors on calls to or from packages explicitly marked as safe by inclusion in <code>@CARP_NOT</code>, or (if that array is empty) <code>@ISA</code>. The ability to override what @ISA says is new in 5.8.</p>

</li>
<li><p>The trust in item 2 is transitive. If A trusts B, and B trusts C, then A trusts C. So if you do not override <code>@ISA</code> with <code>@CARP_NOT</code>, then this trust relationship is identical to, &quot;inherits from&quot;.</p>

</li>
<li><p>Any call from an internal Perl module is safe. (Nothing keeps user modules from marking themselves as internal to Perl, but this practice is discouraged.)</p>

</li>
<li><p>Any call to Perl&#39;s warning system (eg Carp itself) is safe. (This rule is what keeps it from reporting the error at the point where you call <code>carp</code> or <code>croak</code>.)</p>

</li>
<li><p><code>$Carp::CarpLevel</code> can be set to skip a fixed number of additional call levels. Using this is not recommended because it is very difficult to get it to behave correctly.</p>

</li>
</ol>

<h2 id="Forcing-a-Stack-Trace"><a class="permalink" href="Carp.html#Forcing-a-Stack-Trace">#</a><a id="Forcing"></a>Forcing a Stack Trace</h2>

<p>As a debugging aid, you can force Carp to treat a croak as a confess and a carp as a cluck across <i>all</i> modules. In other words, force a detailed stack trace to be given. This can be very helpful when trying to understand why, or from where, a warning or error is being generated.</p>

<p>This feature is enabled by &#39;importing&#39; the non-existent symbol &#39;verbose&#39;. You would typically enable it by saying</p>

<pre><code class="plaintext">perl -MCarp=verbose script.pl</code></pre>

<p>or by including the string <code>-MCarp=verbose</code> in the PERL5OPT environment variable.</p>

<p>Alternately, you can set the global variable <code>$Carp::Verbose</code> to true. See the <code>GLOBAL VARIABLES</code> section below.</p>

<h2 id="Stack-Trace-formatting"><a class="permalink" href="Carp.html#Stack-Trace-formatting">#</a><a id="Stack"></a>Stack Trace formatting</h2>

<p>At each stack level, the subroutine&#39;s name is displayed along with its parameters. For simple scalars, this is sufficient. For complex data types, such as objects and other references, this can simply display <code>&#39;HASH(0x1ab36d8)&#39;</code>.</p>

<p>Carp gives two ways to control this.</p>

<ol>

<li><p>For objects, a method, <code>CARP_TRACE</code>, will be called, if it exists. If this method doesn&#39;t exist, or it recurses into <code>Carp</code>, or it otherwise throws an exception, this is skipped, and Carp moves on to the next option, otherwise checking stops and the string returned is used. It is recommended that the object&#39;s type is part of the string to make debugging easier.</p>

</li>
<li><p>For any type of reference, <code>$Carp::RefArgFormatter</code> is checked (see below). This variable is expected to be a code reference, and the current parameter is passed in. If this function doesn&#39;t exist (the variable is undef), or it recurses into <code>Carp</code>, or it otherwise throws an exception, this is skipped, and Carp moves on to the next option, otherwise checking stops and the string returned is used.</p>

</li>
<li><p>Otherwise, if neither <code>CARP_TRACE</code> nor <code>$Carp::RefArgFormatter</code> is available, stringify the value ignoring any overloading.</p>

</li>
</ol>

<h1 id="GLOBAL-VARIABLES"><a class="permalink" href="Carp.html#GLOBAL-VARIABLES">#</a><a id="GLOBAL"></a>GLOBAL VARIABLES</h1>

<h2 id="$Carp::MaxEvalLen"><a class="permalink" href="Carp.html#$Carp::MaxEvalLen">#</a><a id="Carp::MaxEvalLen"></a>$Carp::MaxEvalLen</h2>

<p>This variable determines how many characters of a string-eval are to be shown in the output. Use a value of <code>0</code> to show all text.</p>

<p>Defaults to <code>0</code>.</p>

<h2 id="$Carp::MaxArgLen"><a class="permalink" href="Carp.html#$Carp::MaxArgLen">#</a><a id="Carp::MaxArgLen"></a>$Carp::MaxArgLen</h2>

<p>This variable determines how many characters of each argument to a function to print. Use a value of <code>0</code> to show the full length of the argument.</p>

<p>Defaults to <code>64</code>.</p>

<h2 id="$Carp::MaxArgNums"><a class="permalink" href="Carp.html#$Carp::MaxArgNums">#</a><a id="Carp::MaxArgNums"></a>$Carp::MaxArgNums</h2>

<p>This variable determines how many arguments to each function to show. Use a false value to show all arguments to a function call. To suppress all arguments, use <code>-1</code> or <code>&#39;0 but true&#39;</code>.</p>

<p>Defaults to <code>8</code>.</p>

<h2 id="$Carp::Verbose"><a class="permalink" href="Carp.html#$Carp::Verbose">#</a><a id="Carp::Verbose"></a>$Carp::Verbose</h2>

<p>This variable makes <code>carp()</code> and <code>croak()</code> generate stack backtraces just like <code>cluck()</code> and <code>confess()</code>. This is how <code>use Carp &#39;verbose&#39;</code> is implemented internally.</p>

<p>Defaults to <code>0</code>.</p>

<h2 id="$Carp::RefArgFormatter"><a class="permalink" href="Carp.html#$Carp::RefArgFormatter">#</a><a id="Carp::RefArgFormatter"></a>$Carp::RefArgFormatter</h2>

<p>This variable sets a general argument formatter to display references. Plain scalars and objects that implement <code>CARP_TRACE</code> will not go through this formatter. Calling <code>Carp</code> from within this function is not supported.</p>

<pre><code>local $Carp::RefArgFormatter = sub {
    require Data::Dumper;
    Data::Dumper-&gt;Dump($_[0]); # not necessarily safe
};</code></pre>

<h2 id="@CARP_NOT"><a class="permalink" href="Carp.html#@CARP_NOT">#</a><a id="CARP_NOT"></a>@CARP_NOT</h2>

<p>This variable, <i>in your package</i>, says which packages are <i>not</i> to be considered as the location of an error. The <code>carp()</code> and <code>cluck()</code> functions will skip over callers when reporting where an error occurred.</p>

<p>NB: This variable must be in the package&#39;s symbol table, thus:</p>

<pre><code># These work
our @CARP_NOT; # file scope
use vars qw(@CARP_NOT); # package scope
@My::Package::CARP_NOT = ... ; # explicit package variable

# These don&#39;t work
sub xyz { ... @CARP_NOT = ... } # w/o declarations above
my @CARP_NOT; # even at top-level</code></pre>

<p>Example of use:</p>

<pre><code>package My::Carping::Package;
use Carp;
our @CARP_NOT;
sub bar     { .... or _error(&#39;Wrong input&#39;) }
sub _error  {
    # temporary control of where&#39;ness, __PACKAGE__ is implicit
    local @CARP_NOT = qw(My::Friendly::Caller);
    carp(@_)
}</code></pre>

<p>This would make <code>Carp</code> report the error as coming from a caller not in <code>My::Carping::Package</code>, nor from <code>My::Friendly::Caller</code>.</p>

<p>Also read the <a href="Carp.html#DESCRIPTION">&quot;DESCRIPTION&quot;</a> section above, about how <code>Carp</code> decides where the error is reported from.</p>

<p>Use <code>@CARP_NOT</code>, instead of <code>$Carp::CarpLevel</code>.</p>

<p>Overrides <code>Carp</code>&#39;s use of <code>@ISA</code>.</p>

<h2 id="%Carp::Internal"><a class="permalink" href="Carp.html#%25Carp::Internal">#</a><a id="Carp::Internal"></a>%Carp::Internal</h2>

<p>This says what packages are internal to Perl. <code>Carp</code> will never report an error as being from a line in a package that is internal to Perl. For example:</p>

<pre><code>$Carp::Internal{ (__PACKAGE__) }++;
# time passes...
sub foo { ... or confess(&quot;whatever&quot;) };</code></pre>

<p>would give a full stack backtrace starting from the first caller outside of __PACKAGE__. (Unless that package was also internal to Perl.)</p>

<h2 id="%Carp::CarpInternal"><a class="permalink" href="Carp.html#%25Carp::CarpInternal">#</a><a id="Carp::CarpInternal"></a>%Carp::CarpInternal</h2>

<p>This says which packages are internal to Perl&#39;s warning system. For generating a full stack backtrace this is the same as being internal to Perl, the stack backtrace will not start inside packages that are listed in <code>%Carp::CarpInternal</code>. But it is slightly different for the summary message generated by <code>carp</code> or <code>croak</code>. There errors will not be reported on any lines that are calling packages in <code>%Carp::CarpInternal</code>.</p>

<p>For example <code>Carp</code> itself is listed in <code>%Carp::CarpInternal</code>. Therefore the full stack backtrace from <code>confess</code> will not start inside of <code>Carp</code>, and the short message from calling <code>croak</code> is not placed on the line where <code>croak</code> was called.</p>

<h2 id="$Carp::CarpLevel"><a class="permalink" href="Carp.html#$Carp::CarpLevel">#</a><a id="Carp::CarpLevel"></a>$Carp::CarpLevel</h2>

<p>This variable determines how many additional call frames are to be skipped that would not otherwise be when reporting where an error occurred on a call to one of <code>Carp</code>&#39;s functions. It is fairly easy to count these call frames on calls that generate a full stack backtrace. However it is much harder to do this accounting for calls that generate a short message. Usually people skip too many call frames. If they are lucky they skip enough that <code>Carp</code> goes all of the way through the call stack, realizes that something is wrong, and then generates a full stack backtrace. If they are unlucky then the error is reported from somewhere misleading very high in the call stack.</p>

<p>Therefore it is best to avoid <code>$Carp::CarpLevel</code>. Instead use <code>@CARP_NOT</code>, <code>%Carp::Internal</code> and <code>%Carp::CarpInternal</code>.</p>

<p>Defaults to <code>0</code>.</p>

<h1 id="BUGS"><a class="permalink" href="Carp.html#BUGS">#</a>BUGS</h1>

<p>The Carp routines don&#39;t handle exception objects currently. If called with a first argument that is a reference, they simply call die() or warn(), as appropriate.</p>

<h1 id="SEE-ALSO"><a class="permalink" href="Carp.html#SEE-ALSO">#</a><a id="SEE"></a>SEE ALSO</h1>

<p><a href="./Carp::Always.html">Carp::Always</a>, <a href="./Carp::Clan.html">Carp::Clan</a></p>

<h1 id="CONTRIBUTING"><a class="permalink" href="Carp.html#CONTRIBUTING">#</a>CONTRIBUTING</h1>

<p><a href="Carp.html">Carp</a> is maintained by the perl 5 porters as part of the core perl 5 version control repository. Please see the <a href="perlhack.html">perlhack</a> perldoc for how to submit patches and contribute to it.</p>

<h1 id="AUTHOR"><a class="permalink" href="Carp.html#AUTHOR">#</a>AUTHOR</h1>

<p>The Carp module first appeared in Larry Wall&#39;s perl 5.000 distribution. Since then it has been modified by several of the perl 5 porters. Andrew Main (Zefram) &lt;zefram@fysh.org&gt; divested Carp into an independent distribution.</p>

<h1 id="COPYRIGHT"><a class="permalink" href="Carp.html#COPYRIGHT">#</a>COPYRIGHT</h1>

<p>Copyright (C) 1994-2013 Larry Wall</p>

<p>Copyright (C) 2011, 2012, 2013 Andrew Main (Zefram) &lt;zefram@fysh.org&gt;</p>

<h1 id="LICENSE"><a class="permalink" href="Carp.html#LICENSE">#</a>LICENSE</h1>

<p>This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.</p>


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